BIOL00T 

LIBRARY 

G 


LABORATORY  OUTLINES 

FOR 

EMBRYOLOGY 


HARMAN 


LABORATORY  OUTLINES 

FOR 

EMBRYOLOGY 


BY 

MARY  T.  HARMAN,  PH.D. 

ASSOCIATE   PROFESSOR   OF  ZOOLOGY,   KANSAS  STATE  AGRICULTURAL  COLLEGE 


SECOND  EDITION 


PHILADELPHIA 

P.  BLAKISTON'S  SON  &  CO. 

1012  WALNUT  STREET 


flOLOGY 
RA 


COPYRIGHT,  1920,  BY  P.  BLAKISTON'S  SON  &  Co. 


PRESS  YORK  PA. 


PREFACE 

These  outlines  were  first  written  for  use  by  students 
in  the  large  laboratory  classes  in  embryology  in  Kansas 
State  Agricultural  College,  and  represented  the  work 
done  (by  those  classes)  during  one  term  (twelve  weeks). 
After  they  were  used  for  two  terms,  they  were  revised, 
parts  rewritten,  and  some  sections  added.  It  is  thought 
that  the  use  of  an  outline  is  the  simplest  means  of  secur- 
ing more  or  less  uniformity  in  the  work  of  the  several 
classes  and,  at  the  same  time,  of  encouraging  the  devel- 
opment of  the  individuality  of  both  the  student  and  the 
teacher.  The  course  is  not  intended  as  an  independent 
one,  but  is  planned  to  supplement  recitation  and  lecture 
work  so  that  the  student  may  obtain  by  observation  a 
general  knowledge  of  the  processes  and  phenomena  of 
development.  The  material  suggested  for  use  in  the 
course  is  such  that,  if  it  is  not  already  at  hand,  it  may  be 
obtained  with  a  minimum  of  difficulty.  The  work  is 
meant  to  be  so  arranged  that  if  time  does  not  permit  the 
use  of  all  parts  of  the  outlines,  some  sections  may  be 
omitted  and  at  the  same  time  preserve  the  continuity  of 
the  course. 

The  author  is  indebted  to  various  authors  for  sug- 
gestions. Those  suggestions  have  been  so  modified  from 
time  to  time  that  it  is  scarcely  possible  to  give  credit  to 


610923 


VI  PREFACE 

any  single  author  for  any  particular  part  of  the  work. 
The  following  books,  however,  have  been  particularly 
helpful: 

The  Development  of  the  Chick,  Lillie. 

Embryology  of  the  Chick  and  the  Pig,  Lillie. 

The  Development  of  the  Human 'Body,  McMurrich. 

Text  Book  of  Embryology,  Hertwig-Mark. 

Elements  of  Embryology,  Foster  &  Balfdur. 

Laboratory  Text  Book  of  Embryology,  Minot. 

A  Manual  of  Histology  and  Organography,  Hill. 

Text  Book  of  Zoology,  Galloway. 

The  Cell  in  Development  and  Inheritance,  Wilson. 

The  author  wishes  to  express  her  gratitude  to  Dr. 
R.  K.  Nabours  for  his  criticism  of  a  part  of  the  manu- 
script and  to  Dr.  Paul  S.  Welch  for  reading  and  criticising 
the  entire  manuscript.  MARY  T.  HARMAN. 


CONTENTS 

CELL  DIVISION i 

THE  SPERMATOZOON ; 3 

THE  EGG 4 

FIXED  AND  STAINED  EMBRYOS — THE  CHICK 15 

THE  PIG  EMBRYO 32 

INDEX.. 45 


vii 


LABORATORY  OUTLINES  FOR 
EMBRYOLOGY 


CELL  DIVISION 

1.  All  organisms  are  composed  of  cells.    The  essential 
parts  of  a  cell  are:  (i)  The  general  cell  substance,  the 
cytoplasm,  and  (2)   a  highly  differential  nucleus.     Most 
cells  have  a  limiting  membrane,  the  cell-wall.    Animal 
cells  may  have  one  or  more  specialized  bodies  lying  near 
or  immediately  inside  the  nucleus,  the  centrosome.    The 
nucleus  may  be  separated  from  the  cytoplasm  by  a  thin 
membrane,  the  nuclear  membrane.    The  substance  of  the 
nucleus  is  composed  of  the  chromatin  material,  which 
stains   readily   with   certain   dyes   and   the   achromatin, 
which  stains  less  readily.     When  the  cell  is  in  the  so- 
called  resting  stage  there  may  be  a  portion  of  the  chromatin 
which  is  larger,  more  compact,  and  stains  more  densely 
than  the  other  chromatin  granules.    This  is  the  chroma- 
tin  nucleolus.     There  may  be  more  than  one  chromatin 
nucleolus. 

Draw  a  cell  in  the  resting  stage  and  label  the  parts. 

2.  When  division  is  about  to  take  place,  the  chromatin 
elements  in  the  nucleus  have  the  appearance  of  a  coiled 
thread,  the  spireme.    The  spireme  is  not  always  a  con- 
tinuous thread.    The  nuclear  membrane  often  disappears 
at  this  stage. 


LABORATORY   OUTLINES   FOR   EMBRYOLOGY 

Draw  a  cell  in  the  tpircme  stage  and  label  the  parts. 

3.  The  spireme  becomes  thicker  and  finally  separates 
into  a  number  of  pieces  called  chromosomes.  The  chro- 
mosomes are  of  different  shapes,  depending  upon  the 
species  of  plant  or  animal.  This  stage  is  known  as  the 
astroid  stage.  If  the  cell  is  an  animal  cell,  the  centrosome 
has  divided  and  the  parts  of  it  have  migrated  to  opposite 
sides  of  the  nucleus.  From  the  centrosomes  as  centers, 
radiations  extend  out  through  the  cell. 

Draw  a  cell  in  the  astroid  and  label  all  the  parts. 

The  process  up  to  this  point  is  known  as  the  prophases 
or  preparation  stages. 

4.  Radiations  extend  across  the  nucleus  from  opposite 
sides.     These  radiations  are  known  as  spindle  fibers.     The 
chromosomes    arrange    themselves   across   the   spindle 
midway  between  the  poles.     Each  chromosome  splits 
longitudinally  into  halves.     This  stage  is  known  as  the 
metaphase  or  middle  stage. 

Draw  a  cell  in  the  metaphase  and  label  all  the  parts. 

5.  One-half  of  each  of  the  chromosomes  passes  along 
the  spindle  fibers  to  one  pole  and  the  other  half  to  the 
other  pole.     When  these  chromosomes  collect  around 
the  poles  they  have  the  appearance  of  a  double  star. 
This  is  called  the  diastroid  stage.     The  diastroid  stage 
and  the  stages  in  which  the  chromosomes  are  between 
the  center  of  the  spindle  and  the  poles  are  known  as  the 
anaphases. 

Draw  a  cell  with  the  chromosomes  some  distance  from 
the  poles.  Label  the  parts.  Draw  a  cell  in  the  diastroid 
stage.  Label  the  parts. 


SPERMATOZOON  3 

6.  After  the  formation  of  the  diasters  the  chromosomes 
unite  to  form  a  spireme  at  each  pole.  From  this  con- 
dition they  change  into  the  resting  stage  or  reticular 
condition.  Coincident  with  the  nuclear  changes,  the 
cytoplasm  may  have  become  constricted  into  masses,  or 
separated  by  the  formation  of  a  wall  perpendicular  to  the 
axis  of  the  spindle.  The  resultant  masses  are  known  as 
daughter  cells.  The  daughter  cells  may  move  apart  or 
remain  in  contact.  These  final  stages  are  known  as  the 
telo  phases. 

Draw  a  telophase  in  which  the  chromatin  is  in  a  spireme 
(di-spireme) .  Label  the  parts.  Draw  two  daughter  cells. 
Label  the  parts. 

The  cell  has  been  followed  through  the  process  of  divi- 
sion, known  as  karyokinesis  or  mitosis.  As  a  result  of  this 
division  there  are  two  cells  instead  of  one.  Write  out 
the  description  of  the  process  of  mitotic  cell  division 
from  the  resting  stage  to  the  daughter  cells. 

THE  SPERMATOZOON 

With  the  high  power  objective  examine  the  slide  of  the 
pig  spermatozoa.  Select  a  single  spermatozoon.  It  is 
composed  of  two  parts,  a  large  ovoid  head  and  a  long  fila- 
mentous tail.  The  anterior  part  of  the  head,  the  head 
cap,  does  not  stain  so  intensely  as  the  remainder  of  it. 
At  the  base  of  the  head  is  a  part  that  stains  very  in- 
tensely. This  is  the  mid-piece.  What  is  the  com- 
parative length  of  the  tail?  • 

Make  a  drawing  of  the  spermatozoon  and  label  all  the 
parts.  <. 


4  LABORATORY   OUTLINES   FOR  EMBRYOLOGY 

THE  EGG 

An  egg  is  a  cell  and  has  all  the  essential  parts  of  a  cell. 
However,  in  the  egg,  some  of  the  parts  have  special 
names.  The  cell-wall  is  called  the  vitelline  membrane; 
the  nucleus  is  called  the  germinal  vesicle;  and  the  nucle- 
olus  is  called  the  germinal  spot.  An  egg  differs  further 
from  most  other  cells  in  that  it  contains  yolk  material. 
This  yolk  material  is  called  deutoplasm. 

-i.  Formation  of  an  Egg 

Eggs  are  produced  by  special  glands  called  ovaries. 
The  ovary  is  covered  by  a  layer  of  cubical  cells  called 
the  germinal  epithelium.  The  eggs  are  formed  from  this 
germinal  epithelium.  Early  in  embryonic  life,  epithe- 
lial buds  or  strings  of  epithelial  cells  grow  down  into  the 
ovary.  Soon  these  buds  lose  their  connection  with  the 
germinal  epithelium  and  form  small  groups  or  nests  of 
cells.  These  groups  or  nests  of  cells  are  known  as  young 
Graafian  follicles.  In  each  follicle  one  cell  takes  a  central 
position  and  is  destined  to  form  the  egg  or  ovum.  The 
egg  increases  rapidly  in  size,  receiving  protection  and 
perhaps  nourishment  from  the  cells  which  surround  it. 
The  cells  which  surround  the  egg  are  known  as  follicular 
cells. 

In  the  section  of  the  cat  ovary,  find  a  young  Graafian 
follicle,  draw  it,  and  label  all  the  parts. 

Only  a  small  number  of  the  young  ova  ripen  and  are 
discharged  as  mature  ova.  Those  which  mature  do  so 


FORMATION   OF   AN  EGG  5 

in  the  following  manner:  The  egg  of  the  young  Graafian 
follicle  grows  until  it  is  a  large  spherical  cell.  The  fol- 
licular  cells  remain  small  and  multiply  rapidly,  forming 
two  layers  of  cells,  between  which  at  one  side  of  the 
follicle  a  cavity  appears.  This  cavity  is  called  the  fol- 
licular  cavity.  As  the  follicle  grows  larger,  this  cavity, 
which  is  eccentric  in  position,  is  filled  with  -a  fluid,  the 
follicular  fluid.  The  cells  composing  the  layer  of  fol- 
licular  cells,  which  immediately  surround  the  egg,  in- 
crease rapidly  in  number  until  there  are  several  layers. 
These  cells  are  known  as  the  discus  proligerus.  The  cells 
external  to  the  follicular  cavity  are  the  stratum  granu- 
losum.  There  are  finally  from  eight  to  twelve  layers  of 
cells  in  the  stratum  granulosum.  The  discus  proligerus 
is  attached  to  the  stratum  granulosum.  The  lighter  area 
immediately  outside  of  the  vitelline  membrane  is  the 
area  pellucida.  The  row  of  cells  of  the  discus  proligerus 
which  radiates  from  the  ovum  is  the  corona  radiata. 

When  the  egg  with  its  surrounding  tissue  has  reached 
this  stage  of  development  it  is  known  as  a  ripe  Graafian 
follicle. 

The  follicle  is  enclosed  by  a  capsule  composed  of  two 
kinds  of  cells.  Those  cells  which  lie  nearest  the  stratum 
granulosum  are  more  or  less  spherical,  and  the  others  are 
rather  elongate.  This  capsule  is  the  theca  folliculi. 
Surrounding  the  theca  folliculi  and  forming  the  sub- 
stance of  the  ovary  are  long,  fibrous  cells,  the  stroma. 

In  the  section  of  the  cat  ovary,  find  a  ripe  Graafian  follicle 
and  draw  it.  Label  all  the  parts. 


6  LABORATORY   OUTLINES    FOR   EMBRYOLOGY 

2.  Maturation 

a.  While  the  egg  is  in  the  Graafian  follicle  the  nucleus 
is  large  and  the  chromatin  is  in  the  so-called  resting  con- 
dition.    The  egg  is  said  to  be  in  the  growth  period.     At 
the  end  of  the  growth  period  it  passes  through  two  suc- 
cessive, modified  mitotic  divisions,  the  maturation  divi- 
sions.    In  the  eggs  of  some  animals  the  maturation 
divisions  occur  before  the  egg  leaves  the  ovary,  but  in 
others  they  do  not  occur  until  afterward.     The  Ascaris 
egg  is  of  the  latter  type. 

On  the  slide  of  Ascaris  find  an  egg  in  the  growth  period. 
Draw  it  and  label  all  the  parts. 

b.  At  the  end  of  the  growth  period,  there  are  half  as 
many  chromatin  masses  as  there  are  somatic  chromo- 
somes.    In  Ascaris  magalocephala  bivalens  there  are  four 
somatic   chromosomes   and,   therefore,   two   chromatin 
masses  at  the  end  of  the  growth  period.     Each  chroma- 
tin  mass  is  made  up  of  four  parts  and  is  called  a  tetrad. 
The  tetrads  arrange  themselves  on  a  spindle  which  is 
comparatively  small  and  is  eccentric  in  position. 

Draw  an  egg  with  the  tetrads  in  the  middle  vf  the  spindle 
(metaphase)  and  label  all  the  parts. 

c.  Each   tetrad  divides  into  two  parts  called  dyads. 
One  dyad  from  each  tetrad  moves  to  one  pole  of  the 
spindle  and  the  other  dyad  moves  to  the  other  pole  of  the 
spindle. 

When  the  dyads  reach  the  poles  the  egg  divides.  The 
resultant  cells  are  very  unequal  in  size.  One  cell  con- 
tains half  of  the  chromatin  and  little  of  the  cytoplasm. 


FERTILIZATION  7 

It  is  the  first  polar  body.  The  other  contains  the  other 
half  of  the  chromatin  and  almost  all  the  cytoplasm.  It 
is  the  secondary  ob'cyte.  The  first  maturation  division  is 
now  completed. 

Without  any  change  in  the  form  of  the  chromatin  ma- 
terial, a  new  spindle  is  formed  in  the  secondary  oocyte. 
The  first  polar  body  may  or  may  not  divide. 

Draw  a  secondary  oocyte  in  a  metaphase  stage  and  label 
all  the  parts. 

d.  Each  dyad  divides  into  two  parts  called  monads. 
One  monad  from  each  dyad  moves  to  one  pole  of  the 
spindle  and  the  other  one  moves  to  the  other  pole  of  the 
spindle. 

Draw  a  secondary  ob'cyte  in  an  anaphase  stage  and  label 
all  the  parts. 

e.  When  the  monads  have  reached  the  poles  there  is 
a  second  unequal  division  of  the  egg.     This  division  is 
similar  to  the  first  one.     The  small  cell  is  the  second 
polar  body  and  the  large  one  is  the  matured  ovum. 

Draw  a  matured  ovum  showing  the  second  polar  body 
and  label  all  the  parts. 

3.  Fertilization 

In  Ascaris  the  spermatozoon  penetrates  the  vitelline 
membrane  before  the  maturation  divisions  occur.  It 
may  be  seen  in  the  cytoplasm  of  the  egg  either  as  an 
indefinite  dark  blotch  or  as  unchanged  in  shape.  After* 
maturation  is  completed  the  chromatin  of  the  egg  changes 
into  the  so-called  resting  condition  and  is  called  the 


8  LABORATORY   OUTLINES   FOR   EMBRYOLOGY 

female  pronucleus.  Coincident  with  the  changes  in  the 
egg  nucleus,  the  spermatozoon  also  changes  into  the  so- 
called  resting  stage  and  is  called  the  male  pronucleus. 
These  two  pronuclei  approach  each  other  and  fuse  to 
form  the  first  segmentation  nucleus. 

Draw  a  cell  showing  the  male  and  female  pronuclei. 
Label  all  the  parts. 

4.  Cleavage 

The  amount  and  distribution  of  the  yolk  is  correlated 
with  the  character  of  the  division  of  the  egg  (segmenta- 
tion, cleavage).  In  eggs,  which,  for  the  most  part,  are 
small  and  contain  a  comparatively  small  amount  of  yolk 
material  (deutoplasm) ,  the  segmentation  is  complete. 
That  is,  the  whole  egg  divides  into  two  daughter  cells. 
This  kind  of  cleavage  is  known  as  total  or  holoblastic 
cleavage. 

If  there  is  a  very  small  amount  of  yolk  and  this  yolk 
almost  uniformly  distributed  throughout  the  cytoplasm, 
the  daughter  cells,  in  general,  are  of  uniform  size.  This 
kind  of  cleavage  is  known  as  equal  cleavage.  Examples  of 
holoblastic  equal  cleavage  are  found  in  the  Echinoder- 
mata,  Amphioxus,  and,  in  general,  in  the  Mammalia. 
If  the  yolk  is  concentrated  more  at  one  pole  than  at  the 
other  and  yet  there  is  not  a  large  amount  of  it,  the  cells 
resulting  from  segmentation  are  unequal  in  size.  This 
kind  of  cleavage  is  known  as  unequal  cleavage.  Ex- 
amples of  holoblastic  unequal  cleavage  are  found  in  the 
Cyclostomata  and  the  Amphibia. 

In  eggs  where  the  amount  of  yolk  is  comparatively 


CLEAVAGE  9 

large,  segmentation  is  incomplete.  This  kind  of  cleavage 
is  called  meroblastic  cleavage.  The  cytoplasm  may  be 
at  one  pole  and  the  greater  part  of  the  egg  composed  of 
deutoplasm.  In  eggs  having  this  distribution  of  yolk 
material,  the  process  of  segmentation  is  confined  to  the 
region  of  the  cytoplasm  and  as  a  result  there  is  formed  a 
cellular  disc.  This  kind  of  cleavage  is  called  discoidal 
cleavage.  Examples  of  meroblastic  discoidal  cleavage  are 
found  in  the  fishes,  reptiles,  and  birds.  In  some  eggs 
the  nucleus  lies  at  the  center  and  when  it  divides  the 
nuclei  thus  formed  migrate  to  the  periphery  and  thus 
the  yolk  becomes  surrounded  by  a  layer  of  cells.  This 
kind  of  cleavage  is  called  peripheral  cleavage.  Examples 
of  meroblastic  peripheral  cleavage  are  found  in  a  number 
of  the  Arthropoda. 

a.  Holoblastic  Cleavage 
(i)  Equal  Cleavage 

On  your  slide  of  the  starfish  eggs  look  for  a  single  un- 
fertilized egg.  The  unfertilized  egg  may  be  recognized 
by  its  large  and  comparatively  clear  nucleus.  These 
eggs  are  large  enough  to  be  seen  with  the  naked  eye. 
Examine  one  first  with  the  low  power  and  then  with  the 
high  power.  How  does  the  germinal  vesicle  compare 
in  size  with  the  whole  egg?  What  difference  in  structure 
do  you  observe  between  the  germinal  vesicle  and  the 
remainder  of  the  egg?  Locate  the  germinal  spot. 

Draw  an  egg  about  one  and  one-half  inches  in  diameter 
and  label  all  the  parts. 

Find  an  egg  which  has  divided.     Can  you  find  a 


10  LABORATORY    OUTLINES    FOR   EMBRYOLOGY 

nucleus  in  each  part?     How  does  the  nucleus  here  differ 
from  the  nucleus  in  the  unfertilized  egg? 

Draw  a  two-celled,  a  four-celled,  and  an  eight-celled 
stage.  Label  all  the  parts.  Make  each  drawing  one  and 
one-half  inches  in  diameter. 

(2)  Unequal  Cleavage 

Examine  a  frog's  egg  which  has  not  divided.  One 
part  of  the  egg  is  dark  and  the  other  part  is  light.  The 
dark  part  of  the  egg  is  the  animal  pole;  the  light  part  is 
the  vegetative  pole.  Is  the  pigment  confined  entirely  to 
one  part  of  the  egg? 

Draw  a  lateral  view  of  an  unsegmented  egg  and  label  the 
parts.  Make  the  drawing  about  an  inch  and  a  half  in 
diameter.  Shade  in  the  pigmented  part. 

Find  a  two«-celled  stage.  How  has  the  division  plane 
divided  the  egg  with  reference  to  the  light  and  dark 
portions?  Is  there  any  difference  in  the  depth  of  the 
segmentation  furrows?  How  do  you  account  for  it? 

Draw   a   two-celled   stage,   lateral   view.    Label   parts. 

Study  a  four-celled  stage.  What  is  the  relation  of  the 
second  cleavage  plane  to  the  first  cleavage  plane?  To 
the  polls  of  the  egg?  How  do  the  cells  compare  in  size? 

Draw  a  four -celled  stage,  view  from  the  animal  pole. 
Label  the  parts. 

Study  an  eight-celled  stage.  What  is  the  relation  of 
the  third  cleavage  plane  to  the  other  two  cleavage 
planes?  To  the  polls  of  the  egg?  What  is  the  com- 
parative size  of  the  cells? 


CLEAVAGE  I I 

Draw  an  eight-celled  stage,  lateral  mew.    Label  the  parts. 

Examine  further  stages  of  division.  What  is  the 
relative  size  of  the  cells  in  the  dark  and  light  hemi- 
spheres? What  is  the  relative  number? 

Examine  an  egg  in  a  many-celled  stage.  With  a  sharp 
scalpel  or  razor  split  the  egg  into  halves  through  the 
poles.  What  is  in  the  center  of  the  egg?  How  many 
layers  of  cells  are  there?  When  an  egg  has  divided  until 
there  are  many  cells  and  these  cells  are  arranged  in  a 
single  layer  so  as  to  form  a  hollow  sphere,  it  is  called  the 
blastula  stage.  The  cavity  in  the  center  of  the  sphere 
is  the  segmentation  cavity. 

Draw  a  section  through  a  blastula  and  label  the  parts. 

Examine  an  egg  which  has  a  small  indentation  on  one 
side.  Where  is  this  indentation  with  reference  to  the 
poles?  With  a  sharp  scalpel  or  razor  split  the  egg  into 
halves  through  this  indentation.  How  are  the  hemi- 
spheres of  this  egg  different  from  the  hemispheres  of  the 
blastula  stage?  What  is  the  form  of  the  segmentation 
cavity  here?  How  many  layers  of  cells  are  there?  The 
cells  at  one  pole  divide  more  rapidly  than  they  do  at  the 
other  pole,  which  results  in  the  folding  in  of  the  cells 
at  one  pole.  Which  pole?  This  process  is  known  as 
gastrulation,  and  the  stage  is  known  as  the  gastrula 
stage.  The  indentation,  or  the  cavity  thus  formed,  is 
called  the  archenteron  or  primitive  gut  cavity.  The 
opening  of  the  archenteron  to  the  outside  is  called  the 
blastopore. 

Draw  a  section  of  a  gastrula  and  label  the  parts. 


12  LABORATORY   OUTLINES   FOR  EMBRYOLOGY 

5.  The  Hen's  Egg 

a.  A  Raw  Egg 

Crack  slightly  the  broad  end  of  a  hen's  egg.  Carefully 
pick  off  a  small  portion  of  the  shell.  Notice  that  beneath 
the  shell  there  is  a  white  leathery  tissue.  This  is  called 
the  shell  membrane.  How  many  layers  are  there  in  the 
shell  membrane?  If  the  egg  is  not  perfectly  fresh,  there 
will  be  a  space  at  this  end  of  the  egg.  This  is  called  the 
air-chamber.  Where  is  the  air-chamber  with  reference 
to  the  shell  and  the  membrane?  Immediately  beneath 
the  shell  membrane  is  the  colorless  albumen,  the  white 
of  the  egg.  Pour  the  egg  out  into  a  saucer.  Examine 
a  piece  of  the  shell  with  the  dissecting  microscope. 
Notice  that  it  is  filled  with  very  small  holes.  What  is 
the  function  of  these  holes  ?  Notice  that  the  white  is  not 
all  of  the  same  consistency.  What  is  the  location  of  the 
more  fluid  part?  From  the  opposite  sides  of  the  colored 
part  of  the  egg,  the  yolk,  extend  two  twisted  chords 
called  the  chalazce  (hail  stones).  Are  they  attached  to 
the  yolk?  Are  they  attached  to  the  shell? 

The  yolk  is  enclosed  in  the  vitelline  membrane.  What 
other  name  could  be  applied  to  the  vitelline  membrane? 
If  the  egg  has  been  fertilized,  there  will  be  at  a  point  on 
the  surface  of  the  yolk,  lying  immediately  underneath  the 
vitelline  membrane,  a  small  white  disc  about  4  m.m.  in 
diameter.  This  is  the  blastoderm.  If  the  egg  has  not 
been  fertilized,  this  spot  will  be  much  smaller.  It 
is  the  nucleus  and  cytoplasm  of  the  cell.  The  blasto- 
derm is  composed  of  a  layer  of  cells.  The  yolk,  as  in  all 
eggs,  is  for  the  nourishment  of  the  developing  embryo. 


A  HARD-BOILED   EGG  13 

Draw  the  egg  as  you  see  it  in  the  saucer.    Label  the  parts. 

Put  a  drop  of  the  yolk  on  a  slide,  add  a  little  water,  and 
examine  it  with  the  microscope.  What  is  the  appearance 
of  the  yolk  granules?  Are  they  uniform  in  size? 

Draw  some  of  the  yolk. 

b.  A  Hard-boiled  Egg 

Break  the  shell  of  a  hard-boiled  egg  and  remove  with- 
out breaking  the  white.  Observe,  again,  the  air-chamber 
and  the  character  of  the  shell  and  the  shell-membrane. 
Try  to  peel  off  the  white  in  thin  layers.  It  will  be  seen 
that  the  white  is  arranged  in  the  form  of  a  spiral.  What 
is  the  direction  of  the  spiral?  Where  is  the  apex  of  the 
spiral?  Peel  off  all  the  white.  Usually  the  vitelline 
membrane  is  also  taken  off  from  the  yolk  with  the  white. 
Observe  the  vitelline  membrane. 

On  one  part  of  the  yolk  there  is  a  disc  that  is  lighter  in 
color  than  the  remainder  of  the  surface  of  the  yolk. 
This  disc  is  called  the  "nucleus  of  Pander."  With  a 
sharp  knife  or  razor  cut  through  the  "nucleus  of  Pander " 
in  such  a  way  as  to  divide  the  yolk  into  two  hemispheres. 
If  the  egg  is  fresh,  it  will  be  seen  that  the  "nucleus  of 
Pander"  is  connected  by  means  of  a  narrow  neck  to  a 
central  portion  of  the  egg  composed  of  similar  material. 
This  is  lighter  in  color  and  is  more  liquid  than  the  other 
yolk.  It  is  composed  of  the  so-called  white-yolk.  The 
darker  yolk  material  is  called  yellow  yolk.  It  will  be 
noticed  that  there  are  alternate  layers  of  white  yolk 
and  yellow  yolk.  How  many  layers  are  there?  Which 


14  LABORATORY   OUTLINES   FOR   EMBRYOLOGY 

layers  are  the  thicker?     Which  forms  the  greater  part 
of  the  yolk,  the  yellow  or  the  white  yolk? 

Draw  the  yolk  hemisphere  and  shade  in  the  yellow  yolk. 
Label  the  Parts. 


c.  An  Egg  Incubated  Three  Days — Live  Embryo 

Open  the  large  end  of  an  egg  which  has  been  incubated 
at  least  three  days.  Notice  that  in  whatever  position 
you  turn  the  egg  the  embryo  is  on  top.  Pour  the  egg 
into  a  dish  containing  normal  salt  solution  which  is  about 
milk  warm.  How  much  of  the  yolk  is  covered  by  the 
blastoderm?  Notice  that  immediately  surrounding  the 
embryo  is  a  light  area.  This  is  called  the  area  pellucida. 
That  part  of  the  blastoderm  extending  beyond  the  area 
pellucida  is  the  area  opaca.  The  part  of  the  area  opaca 
which  contains  the  blood  vessels  is  the  area  vasculosa. 
What  part  of  the  area  opaca  is  occupied  by  the  area 
vasculosa?  What  is  the  shape  of  the  heart?  How  fast 
does  it  beat?  The  vessels  carrying  the  blood  into  the 
heart  are  the  mtelline  veins.  How  many  vitelline  veins 
are  there?  The  blood  is  carried  from  the  embryo  to  the 
vascular  area  by  means  of  the  mtelline  arteries.  How 
many  vitelline  arteries  are  there?  How  does  the  blood 
get  from  the  heart  into  the  vitelline  arteries?  What  is 
the  shape  of  the  embryo?  What  are  the  differences 
between  the  yolk  of  this  egg  and  the  yolk  of  the  fresh  egg? 
What  are  the  differences  in  the  white? 

Draw  the  embryo  showing  its  relation  to  the  yolk.  Label 
the  parts. 


FIXED   AND    STAINED   EMBRYOS — THE   CHICK  15 

FIXED  AND  STAIND  EMBRYOS— THE  CHICK 

i.  Embryo  with  from  Three  to  Six  Mesoblastic  Somites 
(Twenty-two  to  Twenty-four  Hours'  Incubation) 

a.  Whole  Mount 

The  darker,  more  deeply  stained  part  is  the  embryo. 
The  blastoderm  extends  beyond  the  embryo.  What  is 
the  shape  of  the  area  pellucida?  What  is  its  compara- 
tive size?  What  is  the  appearance  of  the  area  opaca? 
Is  the  area  vasculosa  present? 

At  the  head  end  of  the  embryo  the  blastoderm  is 
folded  back  under  the  embryo  for  a  short  distance. 
This  fold  is  called  the  head-fold.  It  lifts  the  head  of 
the  embryo  from  the  yolk.  On  either  side  of  the  middle 
of  the  embryo,  extending  longitudinally,  are  two  thick- 
ened plates.  In  the  head  region  they  come  almost  to- 
gether, but  they  diverge  or  spread  out  nearly  flat  toward 
the  tail.  These  thickened  plates  are  called  the  neural 
plates,  and-the  groove  between  them  is  called  the  neural 
groove.  The  anterior  end  of  these  neural  plates  will  form 
the  brain  and  the  remainder  will  form  the  spinal  cord. 
Lying  beneath  this  neural  groove  is  a  thickened  cord 
of  cells,  called  the  notochord.  Does  the  notochord  extend 
the  entire  length  of  the  neural  groove?  Beneath*  the 
neural  plates,  or  a  little  to  either  side  of  them,  are  from 
three  to  six  pairs  of  more  or  less  cubical  thickenings. 
These  are  called  the  mesoblastic  somites.  How  many 
mesoblastic  somites  in  your  embryo?  The  plate  of  cells 
extending  tailward  from  the  mesoblastic  somites  is 
called  the  segmental  plate.  With  the  increase  in  develop- 


1 6  LABORATORY   OUTLINES   FOR  EMBRYOLOGY 

ment  of  the  embryo  more  mesoblastic  somites  will  be 
formed  from  the  segmental  plates.  The  posterior 
region  of  the  embryo,  where  the  neural  plates,  the  seg- 
mental plates,  and  the  notochord  are  indistinguishable, 
is  the  primitive  streak.  Are  there  any  blood  vessels? 

Make  a  drawing  of  the  twenty-four-hour  whole  mountj 
showing  the  things  described.  Label  the  parts.  Make 
your  drawing  large  enough  so  that  it  will  almost  fill  the  page. 

2.  Embryo  with  from  Ten  to  Sixteen  Mesoblastic  Somites 
(Thirty-three  to  Thirty -eight  Hours'  Incubation) 

a.  Whole  Mount 

What  is  the  shape  of  the  area  peleucida?  What 
changes  have  taken  place  in  the  area  opaca?  The 
irregular,  darkly  staining  parts  of  the  area  opaca  are 
blood-islands.  This,  is  the  beginning  of  the  formation  of 
the  vascular  area.  How  does  the  head-fold  differ  from 
the  head-fold  in  the  twenty-four  hour  chick ?  The  neural 
folds  have  united  in  the  median  line  of  the  body  and 
formed  a  tube,  the  neural  tube.  How  far  back  is  the 
neural  tube  closed?  The  anterior  end  of  the  neural  tube 
is  considerably  enlarged.  This  enlarged  part  is  the  fore- 
brain.  The  parts  of  the  fore-brain  that  project  out  on 
either  side  are  the  optic  vesicles.  Posterior  to  the  fore- 
brain  is  a  second  enlargement  of  the  neural  tube.  It  is 
not  so  large  as  the  fore-brain.  This  is  the  mid-brain. 
Posterior  to  the  mid-brain  are  a  few  enlargements  of 
the  neural  tube,  which  constitute  the  hind-brain.  The 
hind-brain  extends  to  and  includes  the  region  of  the 


CHICK,    33    TO   38   HOURS     INCUBATION  17 

third  mesoblastic  somite.  The  remainder  of  the  neural 
tube  is  the  spinal  cord  or  my  don. 

What  is  the  number  of  the  mesoblastic  somites? 
What  change  has  taken  place  in  the  primitive  streak? 
Locate  the  notochord. 

The  heart  lies  ventral  to  the  hind-brain.  What  shape 
is  it?  What  is  the  comparative^ size?  The  two  broad 
tubes  which  are  connected  with  the  posterior  end  of  the 
heart  are  the  vitelline  veins.  A  single  tube  is  connected 
with  the  heart  at  the  anterior  end.  This  is  the  ventral 
aorta.  Remember  that  veins  always  carry  blood  toward 
the  heart  and  arteries  carry  blood  away  from  the  heart. 

Make  a  drawing  of  the  thirty-six  hour  whole  amount  and 
label  all  the  parts. 

b.  Transverse  Sections 

Sections  cut  perpendicular  to  the  long  axis  of  the  body 
are  transverse  sections.  It  is  very  difficult  to  cut  sections 
so  that  they  are  exactly  perpendicular  to  a  given  plane. 
Many  of  the  sections  labeled  transverse  sections  are 
tipped  a  little  to  one  side  or  the  other.  The  sections  are 
cut  of  uniform  thickness  and  arranged  in  regular  order. 
Those  on  most  of  your  slides  are  fifteen  microns  thick. 
A  micron  is  one-thousandth  of  a  millimeter.  By  count- 
ing the  number  of  sections  in  a  series  the  exact  length  of 
the  embryo  may  be  calculated,  provided  no  sections  have 
been  lost.  The  position  of  any  section  may  be  ascer- 
tained by  determining  its  Dumber  in  the  series.  In  a 
transverse  section  of  a  chick  embryo  there  are  found  three 
kinds  of  cells,  and  these  different  kinds  of  cells  are  ar- 

s 


1 8  LABORATORY   OUTLINES   FOR  EMBRYOLOGY 

ranged  in  layers  which  are  more  or  less  definite.  These 
layers  of  cells  are  called  germ  layers.  The  germ  layer 
lying  next  to  the  yolk  is  composed  of  rather  large, 
rounded  cells.  This  germ  layer  is  the  endoderm  or 
hypoblast.  The  one  lying  next  to  the  shell  and  farthest 
away  from  the  yolk  is  composed  of  cuboidal  and  colum- 
nar cells,  and  is  called  the  ectoderm  or  epiblast.  The  one 
between  the  ectoderm  and  the  endoderm  is  composed 
of  irregular  cells,  and  is  called  mesoderm  or  mesoblast. 
All  of  the  organs  of  the  body  are  formed  from  these  three 
germ  layers.  Most  of  these  organs  are  differentiated 
from  regions  of  unequal  growth  with  a  consequent  fold- 
ing. If  this  folding  is  toward  the  inner  part  of  the  body, 
it  is  called  an  imagination]  if  it  is  outward  from  the  body, 
it  is  called  an  evagination. 

The  section  should  be  studied  with  the  low  power  of 
the  microscope  unless  otherwise  indicated.  Make  out- 
line drawings  with  hard  pencil  and  use  different  colors 
to  represent  the  germ  layers.  For  the  sake  of  uniform- 
ity, color  the  ectoderm  blue,  the  mesoderm  red,  and  the 
endoderm  green.  Do  not  draw  the  cells.  Indicate  on 
your  drawing  of  the  whole  mount  the  location  of  each 
section. 

(i)  Through  the  Fore-brain  Showing  the  Optic  Vesicles 

The  head  is  free  from  the  blastoderm.  How  has  this 
separation  been  brought  about?  Of  what  germ  layers 
is  the  blastoderm  composed?  The  mesoderm  is  in  two 
layers,  one  lying  next  to  the  ectoderm  and  the  other 
lying  next  to  the  endoderm.  The  layer  of  ectoderm  with 


CHICK,  33  TO  38  HOURS'  INCUBATION  19 

the  mesoderm  which  lies  next  to  it  forms  the  somato- 
pleure,  and  the  endoderm  with  the  mesoderm  lying  next 
to  it  forms  the  splanchnopleure.  The  space  or  cavity 
between  the  splanchnopleure  and  the  somatopleure  is  the 
body  cavity.  If  the  body  cavity  is  in  the  embryo,  it  is 
called  the  embryonic  body  cavity  or  ccdome.  If  it  is  in  the 
blastoderm  and  not  in  the  embryo,  it  is  called  the  extra- 
embryonic  body  cavity.  Is  there  a  ccelome  in  the  section 
in  the  region  of  the  fore-brain?  The  ectoderm  forms 
the  outer  covering  of  the  head.  Is  it  of  uniform  thick- 
ness? If  not,  where  is  it  thickest?  The  fore-brain  is 
ectodermal  in  origin.  The  optic  vesicles  are  evaginations 
from  either  side  of  the  fore-brain  and  are  continuous  with 
it.  Is  the  cavity  of  the  fore-brain  continuous  with  the 
cavities  of  the  optic  vesicles?  Is  there  any  mesoderm  in 
this  section?  If  so,  where?  What  part  is  endoderm? 
It  will  be  observed  that  the  extra-embryonic  blood 
vessels  are,  for  the  most  part,  in  the  mesoderm  of  the 
splanchnopleure . 

Draw  the  section  and  label  all  the  parts.  Color  the 
germ  layers. 

(2)  Through  the  Middle  of  the  Heart 

What  is  the  shape  of  the  heart  in  cross  section  ?  Com- 
parative size?  The  heart  is  mesodermal  in  origin.  The 
inner,  thin  layer  of  cells  is  the  endocardium  and  forms  the 
endothelial  lining  of  the  heart.  The  outer,  thicker  layer 
is  the  myocardium  and  forms  the  muscle  of  the  heart.  In 
the  splanchnic  layer  of  mesoderm  are  numerous  spaces. 


2O  LABORATORY   OUTLINES   FOR   EMBRYOLOGY 

These  are  cross  sections  of  extra-embryonic  blood  vessels. 
Dorsal  to  the  heart  is  a  rather  large  cavity,  bounded 
ventrally  by  a  thick  wall  and  dorsally  by  a  thin  one. 
This  is  a  portion  of  the  fore-gut,  the  pharynx.  The 
pharynx  is  lined  with  endoderm.  In  the  median  line  of 
the  body,  dorsal  to  the  pharynx,  is  a  circular  mass  of 
cells,  the  notochord.  The  notochord  is  endoderm.  On 
each  side  of  the  notochord  and  dorsal  to  the  pharynx 
is  a  rather  large  cavity.  These  are  dorsal  aortce.  Why 
is  there  no  ventral  aorta?  All  blood  vessels  are  formed 
in  mesoderm.  What  is  the  neural  tube  called  in  this 
region?  The  ectoderm  of  the  outside  of  the  body  is  con- 
tinuous with  the  ectoderm  of  the  blastoderm.  Is  the 
ccelome  separated  from  the  extraembryonic  body  cavity? 
Draw  the  section,  label  all  the  parts,  and  color  the  germ 
layers. 

(3)  Through  the  Region  of  the  Mesoblastic  Somites 

The  mesoblastic  somites  are  on  either  side  of  the  neural 
tube.  They  are  blocks  of  mesodermal  cells  which  radiate 
from  a  common  central  point.  Connecting  each  meso- 
blastic somite  with  the  mesoderm  of  the  somatopleure 
and  the  splanchnopleure  is  a  neck  of  cells.  This  neck  of 
cells  is  the  intermediate  cell  mass  or  nephrotome.  The 
mesodermic  layers  of  the  splanchnopleure  and  the 
somatopleure  are  called  the  lateral  plates.  Compare  the 
size  of  the  dorsal  aortae  here  with  those  in  section  (i). 

Draw  the  section,  label  all  the  parts,  and,  color  the  germ 
layers. 


CHICK,    44   TO   48   HOURS'    INCUBATION  21 

(4)  Through  the  Primitive  Streak 

Is  the  notochord  present?  Are  the  dorsal  aortae 
present?  In  the  median  portion  of  the  body  the  germ 
layers  cannot  be  distinguished. 

Draw  the  section,  label  the  parts,  and  color  the  germ 
layers.  Color  black  the  portion  in  which  the  germ  layers 

cannot  be  distinguished. 

^ 

c.  Reconstructions 

( i)  Circulatory  System 

In  your  sections  of  the  thirty-six-hour  chick  find  the 
most  anterior  one  which  contains  the  blood  vessels. 
Trace  these  blood  vessels  through  the  remainder  of  the 
sections  several  times.  Beginning  at  the  anterior  end, 
sketch  in  outline  all  the  blood  vessels  in  every  third 
section.  Make  all  your  sketches  on  the  same  scale  and 
keep  them  in  regular  order.  Think  of  these  sections 
placed  one  upon  the  top  of  the  other  in  regular  order. 

From  your  sketches  make  a  diagram  of  the  circulatory 
system  and  label  all  the  parts. 

3.  Embryo  with  from  Twenty -four  to  Twenty-nine  Meso- 
blastic  Somites  (Forty-four  to  Forty-eight  Hours'  In- 
Incubation) 

a.  Whole  Mount 

It  will  be  observed  that  a  number  of  striking  changes 
have  taken  place.  These  are  most  noticeable  in  the 
head  region.  In  the  region  of  the  mid-brain  the  head 
has  become  bent  so  that  the  fore-brain  and  a  portion  of 


22  LABORATORY   OUTLINES    FOR   EMBRYOLOGY 

the  mid-brain  form  a  right  angle  with  the  rest  of  the  head. 
This  bend  is  called  the  cephalic  flexure.  The  head  is  now 
completely  separated  from  the  blastoderm,  and  the  body, 
which  has  been  continuous  with  it  on  the  sides,  is  partly 
separated  from  it  by  the  lateral  folds,  which  unite  with  the 
head  fold.  The  body  has  become  twisted  a  short  dis- 
tance back  of  the  region  of  the  heart,  so  that  the  head  is 
now  lying  on  its  side.  Which  side?  Gan  you  see  both 
optic  vesicles?  Why?  Compare  the  size  of  the  optic 
vesicles  with  that  of  the  fore-brain.  What  were  their 
relative  sizes  in  the  thirty-six-hour  chick?  The  outer 
part  of  the  optic  vesicle  has  invaginated  into  the  original 
cavity  and  has  thus  formed  a  cup,  the  optic  cup.  The 
walls  of  this  double  cup  form  the  two  layers  of  the  retina, 
which  may  be  seen  at  this  time.  What  is  the  compara- 
tive thickness  of  these  two  layers?  The  place  where  the 
rim  of  the  cup  does  not  appear  to  be  continuous  is  the 
choroid  fissure.  The  outside  ectoderm  in  the  region  of 
the  optic  cup  has  thickened  and  formed  an  invagination 
into  the  optic  cup.  This  is  the  lens.  It  appears  as  a 
sphere  lying  in  the  optic  cup.  In  the  region  of  the  hind- 
brain  is  an  invagination  from  the  outside  ectoderm.  This 
is  the  auditory  vesicle. 

The  heart  has  elongated  more  rapidly  than  the  body, 
consequently  it  has  become  twisted  upon  itself.  The 
vitelline  veins  are  in  the  lateral  folds  of  the  blastoderm. 
About  half  way  between  the  vitelline  veins  and  the  end  of 
the  tail  are  two  blood  vessels  extending  from  the  embryo 
into  the  blastoderm.  These  are  vitelline  arteries.  They 
carry  the  blood  from  the  dorsal  aortae  to  the  blastoderm. 


CHICK,    33    TO   38   HOURS'"    INCUBATION  23 

Between  the  hind-brain  and  the  heart  in  the  region  of 
the  pharynx  are  two  or  three  pouches  or  clefts.  These 
are  invaginations  from  the  outside  ectoderm.  Immedi- 
ately beneath  each  pouch  is  an  evagination  from  the 
pharynx.  These  are  the  gill- slits  (visceral  clefts  or 
pouches).  Each  cleft  is  bounded  on  either  side  by  a 
thicker  mass.  These  masses  are  the  arches.  They 
number  from  the  anterior  end.  The  first  arch  is  the 
mandibular  arch.  The  second  arch  is  the  hyoid  arch. 
The  hyomandibular  cleft  is  between  the  mandibular  arch 
and  the  hyoid  arch.  It  is  the  first  visceral  cleft.  The 
other  clefts  and  arches  are  numbered  in  order.  Ventral 
to  the  mandibular  arch  and  beneath  the  optic  vesicle 
is  a  pit  or  invagination  from  the  outside  ectoderm.  This 
marks  the  location  of  the  future  mouth  and  is  called  the 
oral  pit. 

How  many  mesoblastic  somites  are  there?  What 
changes  have  taken  place  in  the  lateral  plates?  In  the 
primitive  streak?  Where  can  you  see  the  notochord? 

Draw  the  forty-eight-hour  whole  mount  and  label  all  the 
parts. 

b.  Transverse  Sections 

;  {.[•••  - 

The  region  from  which  is  taken  the  cross  section  of 
which  you  make  a  drawing,  should  always  be  located  on 
your  drawing  of  the  whole  mount. 

(1)  Through  the  Optic  Vesicle  showing  the  Lens,  the  Choroid  Fissure, 
and  the  Connection  between  the  Optic  Vesicle  and  the  Fore-brain  (the 
Optic  Stalk) 

Because  of  the  cephalic  flexure,  the  plane  of  this  section 


24  LABORATORY   OUTLINES   FOR   EMBRYOLOGY 

passes  through  the  body  twice,  the  fore-brain  and  the 
hind-brain.  The  ventral  sides  of  the  two  parts  lie  to- 
gether. Of  what  germ  layer  is  the  brain  formed?  The 
optic  vesicle?  The  lens?  The  outer  covering  of  the 
body  is  ectoderm.  The  part  of  the  body  in  which  the 
fore-brain  is  located  is  enclosed  in  two  membranes,  and 
the  part  in  which  the  hind-brain  is  located  is  almost,  if 
not  entirely,  enclosed  in  these  two  membranes.  The 
membrane  next  to  the  body  is  the  amnion  and  is  com- 
posed of  two  layers  of  cells:  an  inner  layer,  the  ectoderm, 
and  an  outer  layer,  the  mesoderm.  On  the  side  next  to 
the  yolk  is  the  yolk  sac,  composed  of  an  inner  layer  of 
mesodermal  cells  and  an  outer  layer  of  endodermal  cells. 
It  should  be  kept  in  mind  that  the  mesoderm  of  the  yolk 
sac  contains  the  blood  vessels.  On  the  side  away  from 
the  yolk  is  the  chorion,  composed  of  an  inner  layer  of 
mesodermal  cells  and  an  outer  layer  of  ectodermal  cells. 
What  is  the  shape  of  the  optic  vesicle  ?•  What  is  the 
relative  thickness  of  the  layers  of  the  optic  vesicle?  Is 
the  lens  a  solid  mass  of  cells?  Is  it  connected  to  the 
outside  ectoderm  or  has  it  become  separated? 

The  hind- brain  may  be  distinguished  from  the  fore- 
brain  and  the  mid-brain  on  account  of  its  thin  roof. 
What  is  the  shape  of  the  pharynx?  The  places  where 
the  outside  ectoderm  comes  almost  in  contact  with  the 
endoderm  of  the  pharynx  are  the  gill  clefts  or  visceral 
clefts.  The  thickened  parts  between  the  visceral  clefts 
are  the  gill  arches  or  visceral  arches.  In  each  visceral 
arch  is  an  aortic  arch  which  carries  blood  from  the  ventral 
aorta  to  the  dorsal  aorta.  Remember  that  the  ventral 


CHICK,    44   TO   48   HOURS'    INCUBATION  25 

aorta  is  always  ventral  to  the  gut  and  that  the  dorsal 
aorta  is  always  dorsal  to  the  gut.  In  this  section,  how 
many  ventral  aortae  are  there?  How  many  dorsal 
aortae?  Dorsal  to  the  dorsal  aorta  and  to  either  side  of 
the  hind-brain  are  the  anterior  cardinal  veins.  The  one 
on  the  right  side  is  the  right  anterior  cardinal  vein  and  the 
one  on  the  left  side  is  the  left  anterior  cardinal  vein. 
Where  is  the  notochord? 

Draw  the  section,  color  the  different  germ  layers,  and 
label  all  the  parts.. 

(2)  Through  the  Hind-brain  showing  the  Auditory  Vesicles 

Identify  all  the  parts  found  in  this  section  that  are 
found  in  the  previous  sections.  Ventral  to  the  fore-brain 
and  between  it  and  the  pharynx  is  an  evagination  from 
the  roof  of  the  oral  pit,  the  hypophysis.  What  is  its 
relation  to  the  brain?  Describe  the  auditory  vesicles. 

Draw  the  section,  color  the  different  germ  layers,  and 
label  all  the  parts. 

(3)  Through  the  Posterior  Portion  of  the  Heart 

The  amnion  encloses  the  embryo  dorsally,  but  not 
ventrally.  What  part  of  the  central  nervous  system  is 
here?  The  mesoblastic  somites  are  no  longer  thickened 
blocks  of  cells,  but  have  differentiated  into  a  somewhat 
thickened  plate  of  cells,  the  myotome  or  muscle- plate, 
and  a  mass  of  cells  which  are  more  or  less  loosely 
packed  together,  the  sclerotome.  What  is  the  size  and 
shape  of  the  gut  in  this  section?  Notice  the  thickened 


26  LABORATORY   OUTLINES   FOR  EMBRYOLOGY 

walls  of  the  ccdome,  or  body  cavity.  How  many  dorsal 
aortae  are  here?  Is  the  ventral  aorta  present  in  this 
section?  Why?  Between  the  body  cavity  and  the 
outside  of  the  body  on  either  side  is  a  blood  vessel.  If 
this  blood  vessel  be  traced  through  the  different  sections, 
it  will  be  seen  that  it  connects  the  cardinal  veins  with  the 
heart.  It  is  the  duct  of  Cuvier.  It  is  formed  by  the 
union  of  the  anterior  and  posterior  cardinal  veins  and 
empties  into  the  heart  near  the  place  where  the  vitelline 
veins  join  the  heart.  Identify  the  myocardium  and  the 
endocardium. 

Draw  the  section,  color  the  different  germ  layers,  and 
label  all  the  parts. 

(4)  Through  the  Embryo  about  Half  Way  between  the  Heart  and  the 
Posterior  End 

Note  the  beginning  of  the  folding  up  of  the  somato- 
pleure  to  form  the  amnion.  The  point  on  each  side 
where  the  lateral  fold  delimits  the  embryonic  from  the 
extra -embryonic  area  is  the  lateral  limiting  sulcus. 
What  is  the  character  of  the  mesoblastic  somites?  How 
have  the  myotome  and  sclerotome  been  formed?  On 
the  dorsal  surface  of  the  nephrotome  is  a  thick  cord  of 
cells  with  a  small  cavity  in  it.  This  is  the  Wolffian 
duct  or  mesonephric  duct.  How  many  dorsal  aortae  are 
there?  Are  the  cardinal  veins  found  in  this  section? 
If  they  are  present,  they  are  called  the  posterior  cardinal 
veins,  ,, 

.;  Draw  the  section,  color  the  different  germ  layers,  and 
label  all  the  parts. 


CHICK,  68  TO  72  HOURS'  INCUBATION  27 

c.  Reconstructions 

1 i)  The  Circulatory  System 

• 

In  your  sections  trace  the  circulatory  system  through 
several  times.  Make  outline  drawings  of  the  blood 
vessels  in  about  every  third  section.  Make  all  your  out- 
line drawings  on  the  same  scale,  keeping  the  relative 
position  and  shape  that  are  seen  in  the  sections.  Keep 
your  drawings  in  consecutive  order. 

From  your  drawings  make  a  diagram  of  the  circulatory 
system  of  the  forty-eight-hour  chick  and  label  all  the  parts. 

What  changes  have  taken  place  in  the  circulation 
between  the  thirty-six-hour  chicken  and  the  forty-eight- 
hour  chicken? 

(2)  The  Central  Nervous  System 

Trace  the  central  nervous  system  through  several 
times.  Make  outline  drawings  of  every  third  section  of 
it.  Think  of  these  sections  as  having  a  definite  thickness 
and  placed  one  upon  the  other  in  regular  order. 

Make  a  diagrammatic  drawing  of  the  central  nervous 
system  and  label  all  the  parts. 

4.  Embryo  with  Thirty-five  to  Thirty-seven  Mesoblastic 
Somites  (Sixty-eight  to  Seventy -two  Hours'  Incuba- 
tion) 

a.  Whole  Mount 

It  will  be  observed  that  the  whole  embryo  is  now  lying 
on  its  side.  There  is  "another  bend  in  the  head  region. 
This  bend  is  in  the  region  of  the  hind-brain  and  is  called 


28  LABORATORY    OUTLINES    FOR   EMBRYOLOGY 

the  nuchal  or  cervical  flexure.  Now  the  region  of  the 
hind-brain  is  the  most  anterior  part  of  the  embryo. 
The  lateral  folds  have  been  completed  and  the  tail  fold 
is  well  formed.  In  the  tail  region  the  digestive  tract 
has  begun  to  fold  off  from  the  yolk  sac.  The  posterior 
part  of  the  digestive  tract  is  called  the  hind- gut.  Ante- 
rior to  the  tail-fold  on  the  ventral  side  of  the  hind- 
gut  is  a  bladder-like  evagination.  This  is  the  allantois. 
The  amnion  has  completely  closed,  dorsally.  The  heart 
is  now  within  the  body.  Can  you  trace  the  twists  of  the 
heart?  What  changes  have  taken  place  in  the  eye? 
The  ear?  How  many  visceral  clefts  are  there?  The 
fore-brain  is  now  composed  of  two  parts:  an  anterior 
part  composed  of  two  lobes,  the  telencephalon ,  and  a  part 
immediately  back  of  this,  the  thalamencephalon  some- 
times called  the  diencephalon.  The  telencephalon  is  the 
rudiment  of  the  cerebral  hemispheres.  Toward  the  ven- 
tral surface  of  the  telencephalon  and  anterior  to  the  eye  is 
an  invagination  from  the  outside  ectoderm,  the  olfactory 
pit.  There  is  a  short  diverticulum  in  the  roof  of  the  thala- 
mencephalon. This  is  the  epiphysis.  The  mid-brain 
forms  the  apex  of  the  cephalic  flexure.  The  mid-brain  is 
the  mesencephalon.  Between  the  mid-brain  and  the 
hind-brain,  the  central  nervous  system  is  considerably 
narrowed.  This  narrow  part  is  the  isthmus.  The  hind- 
brain  is  composed  of  two  parts,  the  metencephalon  and 
the  myelencephalon.  The  metencephalon  is  the  most 
anterior  part  of  the  hind-brain  and  is  the  rudiment  of 
the  cerebellum.  The  myelencephalon  has  a  thin  roof 
and  sides.  It  is  the  rudiment  of  the  medulla  oblongata. 


CHICK,  68  TO  72  HOURS'  INCUBATION  29 

Draw  the  seventy-two-hour  whole  mount  and  label  all 
the  parts. 

b.  Transverse  Sections 

Study  your  sections  and  on  your  drawing  of  the  whole 
mount  indicate  the  angle  at  which  they  have  been  cut. 

1 i)  Through  the  Auditory  Vesicle 

This  section  passes  through  the  body  twice.  Why? 
Are  the  two  parts  of  the  body  separate  or  continuous? 
What  portions  of  the  central  nervous  system  are  shown 
in  each  part?  What  blood  vessels  are  seen  in  this 
section?  If  you  cannot  tell  by  looking  at  only  the  one 
section,  trace  them  through  and  compare  with  the  blood 
vessels  in  your  sections  of  the  forty-eight-hour  chick. 
Between  the  floor  of  the  hind-brain  and  auditory  vesicle 
may  be  seen  the  ganglion  complex  of  the  seventh  and 
eighth  cranial  nerves,  the  acustico-facialis  ganglion. 
Above  the  third  aortic  arch  and  ventral  to  the  auditory 
vesicle  is  the  ganglion  of  the  ninth  cranial  nerve,  the 
glosso-pharyngeal  ganglion. 

Draw  the  section,  color  the  different  germ  layers,  and 
label  all  parts. 

(2)  Through  the  Optic  Vesicle 

Your  section  should  be  selected  so  that  it  will  show,  if 
possible,  the  choroid  fissure,  the  lens,  and  the  optic  stalk. 
What  part  of  the  fore-brain  is  in  your  section?  A  part 
of  the  hind-brain  also  may  be  in  the  section.  What 
is  the  relative  position  of  the  different  parts  of  the  brain  ? 


30  LABORATORY   OUTLINES   FOR  EMBRYOLOGY 

What  is  the  shape  of  the  lens?  Of  how  many  layers  of 
cells  is  it  composed?  Identify  all  the  blood  vessels. 
Are  the  Wolffian  ducts  present?  If  present,  where  are 
they?  What  has  become  of  the  mesoblastic  somites? 
The  fore-gut  may  have  two  diverticula,  one  on  either  side 
of  the  ventral  part.  These  are  the  lung-buds. 

Draw  the  section,  color  the  different  germ  layers,  and 
label  all  the  parts. 

(3)  Through  the  Olfactory  Pits 

Where  are  the  olfactory  pits  with  reference  to  the  fore- 
brain?  Does  this  section  pass  through  the  mid-brain? 
Identify  all  the  blood  vessels  in  the  section.  The  rather 
elongated  ventral  evagination  from  the  fore-gut  is  the 
first  liver  diverticulum.  Find  the  Wolffian  ducts.  Near 
the  Wolffian  ducts  are  one  or  more  rather  thickened 
tubules.  These  are  the  beginnings  of  the  Wolffian 
bodies.  It  will  be  seen  that  the  gut  and  the  tissue  imme- 
diately surrounding  it  are  connected  to  the  body  dor- 
sally  by  a  neck  of  tissue.  This  neck  of  tissue  is  the  dorsal 
mesentery.  There  is  also  a  short  neck  of  tissue  ventral 
to  the  gut.  This  is  the  ventral  mesentery.  The  thick  en- 
ings  of  the  body  wall  to  the  side  of  the  posterior  part  of 
the  body  cavity  are  the  fore-limb  buds. 

Draw  the  section,  color  the  different  germ  layers,  and 
label  all  the  parts. 

(4)  Through  the  Allantois  Where  it  is  Connected  with  the  Hind-gut 

The  allantois  is  a  bladder-like  evagination  from  the 
ventral  side  of  the  posterior  part  of  the  hind-gut.  What 


CHICK,  68  TO  72  HOURS'  INCUBATION  31 

is  its  shape  in  the  section?  Is  the  body  closed  ventrally? 
What  is  the  shape  of  the  body  cavity?  Locate  the  Wolf- 
fian  ducts.  Are  the  Wolffian  bodies  in  this  section? 
The  thickening  of  the  body  wall  to  the  sides  of  the  body 
cavity  are  the  hind-limb  buds.  Does  the  amniori  entirely 
enclose  the  body? 

Draw  the  section,  color  the  different  germ  layers,  and 
label  all  the  parts. 

c.  Reconstruction 

(i)  The  Alimentary  Tract  and  Its  Appendages 

Beginning  with  the  most  anterior  part,  trace  the  ali- 
mentary tract  through  all  the  sections.  It  will  be  seen 
that  from  the  most  anterior  part  to  the  region  of  the 
vitelline  veins  it  is  an  irregular  tube.  This  part  of  it  is 
the  fore-gut.  From  the  fore-gut  posteriorly  for  about  a 
third  or  a  fourth  of  the  length  of  the  embryo  the  alimen- 
tary tract  is  continuous  with  the  yolk  sac.  In  the  poste- 
rior part  it  again  forms  a  tube,  the  hind-gut.  The 
alimentary  tract  continues  to  fold  off  from  the  yolk  sac 
until  the  fore-gut  and  the  hind-gut  meet.  They  meet  in 
-  the  posterior  part  of  the  duodenum.  The  most  anterior 
part  of  the  fore-gut,  that  is,  the  portion  beneath  the 
fore-brain,  is  comparatively  small.  This  is  the  hypoph- 
ysis. Suddenly  it  becomes  very  large  and  irregular. 
The  lateral  irregularities  are  the  visceral  pouches  and 
clefts.  How  many?  Ventral  to  the  second  visceral 
pouch  is  a  long,  narrow  evagination,  the  thyroid  gland. 
The  pharynx  becomes  flattened  laterally  to  form  the 
trachea,  and  then  the  lung-buds  are  given  off.  Poste- 


32  LABORATORY    OUTLINES   FOR   EMBRYOLOGY 

rior  to  the  lung-buds  the  gut  narrows  into  the  short 
oesophagus.  Soon  it  enlarges  somewhat  to  form  the 
stomach.  The  ventral  evagination  of  the  duodenum  is 
the  liver.  In  the  hind-gut  the  ventral  bladder-like 
evagination,  as  was  mentioned  before,  is  the  allantois. 

From  your  study  of  these  sections,  reconstruct  the  ali- 
mentary tract  and  its  appendages  and  make  a  drawing  of 
it  as  an  opaque  object,  lateral  mew. 


THE  PIG  EMBRYO 
i.  Ten-millimeter  Embryo 

a.  Whole  Embryo 

Remove  all  the  membranes  from  a  ten-millimeter  pig 
embryo.  Examine  the  external  form  with  the  dissecting 
microscope  or  the  hand  lens.  It  will  be  noticed  that  the 
head  is  very  large  in  comparison  with  the  body.  It 
forms  nearly  a  right  angle  with  the  remainder  of  the 
body.  This  marks  the  location  of  the  hind-brain.  An- 
terior to  the  hind-brain  is  an  enlarged  part  which  makes  a 
rounded  angle.  This  marks  the  position  of  the  mid- 
brain.  The  fore-brain  is  now  composed  of  two  rounded 
lobes,  the  rudiments  of  the  cerebral  hemispheres.  In  the 
angle  ventral  to  the  fore-brain  and  the  mid-brain  is  the 
lens  of  the  eye  surrounded  by  the  edges  of  the  optic  cup. 
Extending  from  the  eye  ventrally  is  a  depression  or 
groove,  the  lachrymal  groove.  The  lachrymal  groove 
leads  to  an  invagination  forming  a  cup-like  pit  ventral 
to  the  anterior  part  of  the  fore-brain.  This  invagination 


PIG    EMBRYO,    TEN-MILLIMETER  33 

is  the  olfactory  pit.  Caudal  to  the  lachrymal  groove  and 
dorsal  to  the  olfactory  pit  is  a  thickened  part,  the  maxil- 
lary process  which  will  form  the  greater  part  of  the  upper 
jaw.  Caudal  to  this  thickening  is  a  second  one,  the 
mandibular  process,  which  will  form  the  lower  jawi  The 
first  gill  cleft  remains  as  a  groove  calidad  to  the  mandibu- 
lar process.  This  marks  the  position  of  the  future  ex- 
ternal auditory  meatus.  The  second,  third  and  fourth 
gill  clefts  have  disappeared  and  their  remains  are  marked 
by  a  triangular  depression,  the  apex  of  which  is  at  the 
ventral  terminus  of  the  first  gill  cleft.  This  depression 
is  the  cervical  sinus. 

Note  that  the  length  of  the  dorsal  side  of  the  embryo 
is  three  or  more  times  the  length  of  the  ventral  side.  On 
the  dorsal  side  from  the  hind-brain  terminating  in  the 
slender  tail  are  a  number  of  segments,  the  muscu  lar 
segments.  On  the  ventral  side  of  the  embryo  is  the 
large  umbilical  cord.  Its  connection  with  the  embryo 
occupies  about  one-third  of  the  ventral  part  of  the 
body  or  almost  all  of  the  ventral  surface  of  the  abdominal 
region  proper.  Anterior  to  the  umbilical  cord  the  cardiac 
region  protrudes  ventrally.  Between  the  cardiac  region 
and  the  muscular  segments  is  a  large  evagination,  the 
fore-limb  bud.  Between  the  posterior  connection  of  the 
umbilical  cord  to  the  body  and  the  origin  of  the  tail  is 
another  smaller  evagination,  the  hind-limb  bud.  Extend- 
ing from  the  fore-limb  bud  to  the  hind-limb  bud  along 
curvature  of  the  body  is  the  milk  ridge. 

Draw  the  whole  embryo  to  scale  and  label  all  the  parts. 


34  LABOKATORY   OUTLINES   FOR   EMBRYOLOGY 

b.  Transverse  Sections 

The  transverse  sections  should  be  parallel  to  the  length 
of  the  hind-brain.  Indicate  on  your  drawing  of  the  whole 
embryo  the  region  from  which  each  section  is  taken. 

1 i)  Through  the  Anterior  Part  of  the  Otocyst 

This  section  passes  through  the  body  twice.  The 
hind-brain  has  a  very  thin  dorsal  wall.  Its  lateral  walls 
have  several  irregular  folds,  the  neuromeres.  The  fore- 
brain  appears  as  an  oval  section  of  the  central  nervous 
system.  On  either  side  of  the  body  near  the  hind-brain 
are  the  otocyst  s.  The  rather  sharp  evagination  of  the 
o  to  cyst  extending  toward  the  hind-brain  is  the  endolym- 
phatic  duct.  Ventral  to  the  otocyst  and  between  it  and 
the  hind-brain  is  the  acustico-facialis  ganglion.  To  the 
side  of  the  hind-brain  and  almost  between  it  and  the 
fore-brain  is  the  large  trigeminal  ganglion.  Dorsal  to 
the  otocyst  and  to  the  side  of  the  hind-brain  is  the  vagus 
ganglion.  Dorsal  to  the  vagus  ganglion  may  be  seen 
fibers  of  the  spinal  accessory  nerve. 

Draw  the  section,  color  the  germ-layers,  and  label  all  the 
parts. 

(2)  Through  the  Choroid  Fissure  and  the  Optic  Stalk 

This  section  passes  through  the  fore-brain  and  the 
spinal  cord.  The  spinal  cord  has  differentiated  into 
two  distinct  zones,  the  dorsal  zone  and  the  ventral  zone. 
From  either  side  of  the  spinal  cord  may  be  seen  the  roots 
of  the  spinal  nerves.  The  notochord  is  small  compared 
with  the  notochord  of  the  chi  cken.  Identify  the  jugular 


TEN-MILLIMETER  35 

vein  on  either  side  of  the  body  ventral  to  the  spinal  cord. 
Near  the  jugular  vein  is  the  united  vagus  and  spinal 
accessory  nerve.  Ventral  to  this  nerve  and  also  near  the 
jugular  vein  is  the  petrosal  ganglion  of  the  ninth  nerve. 
Identify  the  gill  clefts  and  gill  arches,  the  carotid  artery, 
the  pharynx,  the  optic  stalk,  the  two  layers  of  the  retina, 
the  choroid  fissure,  the  lens,  the  cerebral  hemispheres. 
Ventral  to  the  first  gill  cleft  is  the  maxillary  nerve. 

Draw  the  section,  color  the  germ  layers,  and  label  all  the 
parts. 

(3)  Through  the  Middle  of  the  Heart  and  the  Fore-limb  Buds 

The  description  of  the  spinal  cord  as  given  in  section 
(2)  will  apply  here  also.  At  the  origin  of  the  limb  bud 
is  a  nerve  plexus,  the  brachial  plexus.  Dorsal  to  the 
brachial  plexus  is  a  blood  vessel,  the  subclavian  vein. 
Ventral  to  the  no  to  chord  and  on  either  side  of  the  median 
line  of  the  body  is  the  dorsal  aorta.  Between  the  two 
dorsal  aortae  and  a  little  ventral  to  them  is  the  oesophagus. 
Ventral  to  the  oesophagus  is  the  trachea.  Ventral  to  the 
limb  buds  and  on  either  side  of  the  trachea  is  a  large 
irregular  blood  vessel,  the  duct  of  Cuvier.  The  heart  is 
now  divided  into  four  chambers,  the  two  auricles  and  the 
two  ventricles.  The  walls  of  the  ventricles  have  become 
thickened  and  now  have  some  of  the  characteristics  of 
heart  tissue.  The  tissue  between  the  two  ventricles  is 
the  ventricular  septum.  The  triangular  pieces  of  tissue 
extending  from  the  dorsal  wall  of  each  ventricle  down 
into  the  cavity  of  the  ventricle  are  the  auricular-ventricu- 
laijalves.  The  cavities  of  the  auricles  are  larger  than 


36  LABORATORY    OUTLINES    FOR   EMBRYOLOGY 

the  cavities  of  the  ventricles  but  the  walls  are  very  much 
thinner.  The  two  auricles  are  separated  dorsally  by  a 
thin  membrane,  the  septum  spurium.  They  are  sepa- 
rated ventrally  by  a  thicker  membrane,  the  continua- 
tion of  the  ventricular  septum. 

Draw  the  section,  color  the  germ  layers,  and  label  all  the 
parts. 

(4)  Through  the  Body  about  Half  Way  between  the  Fore-limb  Buds 
and  the  Hind-limb  Buds 

This  section  passes  through  the  umbilical  cord.  The 
description  of  the  spinal  cord  given  in  section  (2)  will 
apply  here.  The  dorsal  aorta  is  a  single  vessel  in  this 
region.  On  either  side  of  the  dorsal  aorta  is  a  large  body 
filled  with  cavities.  These  bodies  are  the  Wolffian  bodies. 
The  part  of  the  digestive  tract  in  this  region  is  the 
stomach.  It  is  connected  to  the  body  dorsally  by  a  neck 
of  mesoderm,  the  major  omentum.  The  mesoderm  con- 
tinuing from  the  stomach  ventrally  is  the  minor  omentum. 
Surrounding  the  stomach  laterally  and  ventrally  are 
four  large  lobes  of  tissue  filled  with  cavities.  These 
masses  of  tissue  are  the  lobes  of  the  liver.  The  large 
blood  vessel  in  the  right  dorsal  lobe  is  the  inferior  vena 
cava.  The  large  blood  vessels  in  the  ventral  lobes  are  the 
umbilical  veins.  .In  the  tissue  between  the  liver  lobes  is  a 
cavity  surrounded  by  a  thickened  wall,  the  gall-bladder. 
Identify  the  umbilical  arteries  in  the  umbilical  cord.  On 
the  ventro-median  surface  of  the  Wolfnan  body,  near  the 
dorsal  end  of  the  major  omentum,  is  a  ridge,  the  genital 
ridge. 


PREGNANT  UTERUS  37 

Draw  the  section,  color  the  germ  layers  and  label  all  the 
arts. 

2.     The  Pregnant  Uterus 

Uteri  containing  embryos  three  or  four  inches  in  length 
may  be  obtained  from  any  large  slaughter  house.  The 
whole  uterus  with  the  ovaries  should  be  secured.  If  they 
are  preserved  and  hardened  for  a  few  days  in  ten  per 
cent,  formalin,  then  transferred  to  three  or  four  per  cent, 
formalin,  and  finally  soaked  in  water  three  or  four  days 
before  using,  they  will  be  well  preserved  and  most  of  the 
disagreeableness  of  the  formalin  preservatives  will  be 
removed.  It  is  well  to  change  the  water  some  two  or 
three  times. 

Examine  the  uterus  and  note  that  it  is  composed  of  two 
rather  large  tubes  united  at  one  end  and  free  at  the  other. 
These  are  called  the  horns  of  the  uterus.  The  horns  are 
united  at  the  vagina.  Along  the  inner  edge  of  each  horn 
is  a  broad,  tough,  flat  membrane  which  causes  the  outer 
edge  to  form  a  ruffle.  This  membrane  is  the  broad 
ligament.  The  location  of  the  embryos  in  the  uterus  is 
indicated  by  the  enlargements.  Note  the  many  branched 
blood  vessels  beneath  the  surface  of  these  enlargements. 
Trace  one  horn  of  the  uterus  to  the  free  end.  It  will  be 
seen  that  the  horn  suddenly  narrows  down  into  a  tube 
which  is  about  the  size  of  a  large  knitting  needle.  This 
tube  is  the  Fallopian  tube  or  oviduct.  The  Fallopian 
tube  ends  distally  in  a  thin  membrane  which  surrounds 
the  ovary,  with  the  exception  of  an  opening  into  the  body 
cavity.  This  terminal  opening  is  the  ostium  tub 03  ab- 


38  LABORATORY    OUTLINES   FOR   EMBRYOLOGY 

dominate.  What  is  the  size  of  the  ovary?  Shape? 
The  large,  colored  irregularities  of  the  ovary  are  the 
recent  corpora  lutea.  How  many  in  each  ovary?  How 
does  the  number  compare  with  the  number  of  embryos 
in  the  uterus?  The  smaller,  rounded  spots  that  re- 
semble blisters  are  Graafian  follicles.  Open  one  of 
the  Graafian  follicles.  What  is  the  nature  of  the 
contents? 

With  a  pair  of  scissors  or  scalpel  remove  one  of  the 
enlargements  by  cutting  mid-way  between  two  of  them. 
Cut  through  the  broad  ligament.  Open  this  part  of  the 
uterus  by  cutting  longitudinally  the  side  opposite  the 
broad  ligament.  This  cut  should  pass  through  the  walls 
of  the  uterus  and  the  outer  embryonic  covering,  the 
chorion.  In  the  pig,  the  chorion  is  composed  of  the 
chorion  proper  and  the  wall  of  the  allantois.  From  one 
side  carefully  separate  the  chorion  from  the  walls  of  the 
uterus.  Note  that  the  inner  layer  of  the  uterine  wall  is 
in  folds  which  extend  around  the  embryo.  Also  note  the 
blood  vessels  in  this  layer.  What  is  the  position  of  the 
chorion  with  reference  to  these  folds?  Carefully  sepa- 
rate the  chorion  from  the  amnion.  The  amnion  is 
semitransparent  and  is  a  much  thinner  membrane  than 
the  chroion.  Note  the  blood  vessels  in  the  chorion. 
(The  blood  vessels  are  in  the  allantoic  wall  of  the  chorion.) 
Compare  them  with  the  blood  vessels  of  the  lining  of  the 
uterus.  Also  note  the  very  small  blood  vessels  of  the 
amnion.  To  the  ventral  side  of  the  embryo  is  the  um- 
bilical cord,  which  connects  the  embryo  to  the  chorion. 

Draw  the  embryo  in  position,  showing  the  blood  vessels 


DISSECTION    OF   THE    PIG    EMBRYO  39 

and  connection  of  the  embryo  to  the  chorion.     Label  all  the 
parts. 

Carefully  remove  the  entire  chorion  from  the  uterus. 
It  will  be  seen  that  the  only  connection  of  the  embryo  to 
the  uterus  is  the  contact  of  the  chorion  and  the  mucous 
lining  of  the  uterus.  Open  the  amnion  on  the  dorsal  side 
of  the  embryo.  It  will  be  seen  that  it  is  not  connected 
with  the  embryo  except  at  the  distal  end  of  the  umbilical 
cord.  How  many  blood  vessels  in  the  umbilical  cord? 
The  blood  vessels  may  be  distinguished  from  the  re 
mainder  of  the  tissue  in  the  umbilical  cord  by  their  dark 
color,  due  to  the  blood  in  them.  The  colorless  tube  in 
the  umbilicus  is  the  allantois. 

3.     The  Dissection  of  the  Embryo 
a.  The  Abdomen 

Cut  away  the  amnion  and  the  chorion  except  for  a 
small  part  at  the  end  of  the  umbilicus.  Open  the  em- 
bryo in  the  mid- ventral  line,  being  careful  to  separate 
the  tissue  from  the  umbilicus.  Do  not  break  any  of  the 
blood  vessels  or  the  allantois.  Pin  back  the  body  wall. 
The  large,  reddish-brown  mass  exposed  is  the  liver. 
Separate  the  blood  vessels  in  the  umbilicus  and  trace 
them  into  the  body.  The  one  going  to  the  liver  is  the 
umbilical  vein.  The  other  two  are  the  umbilical  arteries. 
Trace  the  allantois  toward  the  posterior  end.  The  en- 
largement of  the  allantois  in  the  pelvic  region  is  the  uri- 
nary bladder.  A  tube  from  either  side  enters  the  bladder 
on  the  dorsal  surface  near  the  posterior  end.  These  are 
the  ureters.  Separate  the  tube  leading  from  the  bladder 


40  LABORATORY    OUTLINES    FOR   EMBRYOLOGY 

^ 

to  the  outside  of  the  body.  This  is  the  urethra.  With- 
out removing  any  of  the  liver,  examine  it.  Of  how  many 
lobes  is  it  composed?  Size?  Position?  Dorsal  to  the 
liver  and  a  little  posterior  to  it  is  the  much  coiled  in- 
testine. Dorsal  to  the  bladder  and  ventral  to  the  ureters 
are  two  fine  tubes,  one  on  either  side,  which  unite  dorsal 
to  the  posterior  end  of  the  bladder.  These  tubes  are 
the  Fallopian  tubes  of  the  female.  The  posterior  part 
of  the  Fallopian  tubes  forms  the  horns  of  the  uterus. 
These  unite  to  form  the  vagina.  If  the  specimen  is  a 
male  the  point  of  union  of  the  remains  of  the  Fallopian 
tubes  form  the  sinus  p  ocular  is,  or  male  uterus.  The 
sex  ducts  of  the  male  are  the  vas  deferens.  Trace  the 
sex  ducts  until  they  open  to  the  exterior.  Near  the  an- 
terior end  of  the  sex  ducts  and  a  little  ventral  to  them  are 
the  sex  glands,  the  ovaries  if  female,  or  the  testes  if  male. 
Dorsal  to  the  sex  glands  and  toward  the  median  line  of 
the  body  are  the  remains  of  the  Wolffian  bodies.  By 
lifting  the  intestine  and  the  posterior  part  of  the  liver,  a 
part  of  the  comparatively  large  kidneys  may  be  seen. 
Trace  the  ureters  to  the  kidneys.  In  the  median  line  of 
the  body,  extending  between  the  sex  ducts  and  posteriorly 
dorsal  to  the  urethra,  is  the  posterior  end  of  the  intestine, 
the  descending  colon  and  the  rectum. 

Draw  the  dissection  and  label  all  the  parts. 

Trace  the  umbilical  vein  through  the  liver  by  carefully 
dissecting  away  a  small  part  of  the  liver  at  a  time.  Im- 
mediately dorsal  to  the  anterior  part  of  the  liver  is  the 
stomach.  What  is  its  shape?  Position?  The  small 
bladder  found  in  the  liver  is  the  gall  bladder.  The  duct 


DISSECTION    OF   THE   PIG   EMBRYO  41 

leading  from  the  gall  bladder  is  the  cystic  duct.  This 
unites  with  another  small  duct,  the  hepatic  duct,  to  form 
the  common  bile  duct.  The  common  bile  duct  empties 
into  the  intestine  a  short  distance  posterior  to  the  pyloric 
end  of  the  stomach.  Lying  along  the  greater  curvature 
of  the  stomach  is  a  dark-colored  body,  the  spleen.  How 
is  it  held  in  position?  Dorsal  to  the  stomach  is  a 
whitish  body,  the  pancreas.  What  is  its  shape?  Posi- 
tion? A  duct  leads  from  the  pancreas  to  the  intestine. 
This  is  the  pancreatic  duct,  or  the  duct  of  Wirsung.  It 
empties  into  the  intestine  near  the  place  where  the  com- 
mon bile  duct  empties  into  the  intestine.  How  is  the 
intestine  held  in  position?  The  connective  tissue  that 
holds  the  intestine  in  position  is  the  mesentery.  Care- 
fully remove  the  mesentery  and  straighten  out  the  in- 
testine. Is  it  a  continuous  tube?  How  long  is  it? 
What  marks  the  transition  from  the  large  to  the  small 
intestine?  Is  there  a  difference  in  size  between  the  large 
and  the  small  intestine?  In  length? 

Trace  the  umbilical  arteries  to  their  origin.  They  are 
branches  of  the  dorsal  aorta.  A  short  distance  from  the 
aorta  the  umbilical  arteries  branch,  one  part  going  to  the 
umbilicus  and  the  other  going  to  the  hind  leg.  The  one 
going  to  the  hind  leg  is  the  iliac  artery.  A  short  distance 
posterior  to  the  origin  of  the  umbilical  arteries  the  aorta 
divides  into  two  parts.  These  are  the  caudal  aortas. 
Trace  the  aorta  to  the  diaphragm.  Note  the  branches 
given  off  to  the  kidneys,  renal  arteries',  to  the  mesentery, 
superior  mesenteric  artery,  to  the  liver,  hepatic  artery, 
and  to  the  stomach,  the  gastric  artery. 


42  LABORATORY   OUTLINES   FOR   EMBRYOLOGY 

Dorsal  to  the  iliac  arteries  are  the  iliac  veins.  They 
unite  to  form  the  ascending  vena  cava.  From  the  kid- 
neys, ventral  to  the  renal  arteries,  the  ascending  vena 
cava  receives  the  renal  veins.  Trace  the  ascending  vena 
cava  to  the  diaphragm.  From  where  does  the  umbilical 
vein  receive  its  blood?  Trace  the  course  of  this  blood 
to  the  heart.  Where  does  the  blood  from  the  intestine 
go? 

Draw  a  diagram  of  the  circulation  thus  far  worked  out 
and  label  all  the  parts.. 

b.  The  Thorax 

What  blood  vessels  pass  through  the  diaphragm? 
The  oesophagus  extends  from  the  stomach  through  the 
diaphragm  into  the  thorax.  Separate  the  diaphragm 
from  the  body  wall.  The  masses  of  tissue  occupying 
the  greater  part  of  the  thoracic  cavity  are  the  lungs. 
How  many  lobes?  Size?  Shape?  Position? 

What  is  the  position  of  the  heart?  Size?  Shape? 
The  heart  is  enclosed  in  a  thin  connective  tissue  sac,  the 
pericardium.  The  point  of  the  heart  is  called  the  apex 
and  the  other  end  is  called  the  base.  The  firm,  muscular 
part  of  the  heart  composes  the  ventricles  and  the  darker 
colored,  softer  portion  at  the  base  composes  the  auricles. 
Both  the  auricles  and  ventricles  are  called  right  and  left, 
according  to  their  position.  Trace  the  aorta  to  the  heart. 
Where  does  it  enter  the  heart?  How  many  arches  has 
the  aorta  now?  The  artery  leading  from  the  ventricle 
to  the  lungs  is  the  pulmonary  artery.  Which  ventricle? 
What  is  the  relation  of  the  pulmonary  artery  to  the 


DISSECTION    OF   THE   PIG   EMBRYO  43 

lungs?  From  the  anterior  part  of  the  arch  of  the  aorta 
arises  a  vessel  which  carries  the  blood  toward  the  head. 
This  vessel  is  the  innominate  artery.  Branches  from  the 
innominate  artery  are  given  off  laterally,  going  to  each 
fore-limb,  the  right  and  left  subclavian  arteries.  Do  you 
find  the  carotid  arteries  leading  from  the  innominate 
artery  to  either  side  of  the  head?  Trace  the  inferior 
Vena  cava  vein  to  the  heart.  With  what  part  of  the 
heart  does  it  connect?  The  superior  vena  cava  and  the 
inferior  vena  cava  empty  into  the  heart  near  the  same 
place.  The  blood  from  the  anterior  part  of  the  body  is 
collected  in  the  superior  vena  cava.  Trace  it  and  its 
branches  to  the  neck  and  fore-legs.  Do  you  find  the 
pulmonary  veins?  The  pulmonary  veins  carry  the 
blood  from  the  lungs  to  the  heart.  What  part  of  the 
heart?  Open  the  heart.  Describe  the  valves  separating 
the  auricles  from  the  ventricles.  The  two  ventricles  are 
separated  by  a  muscular  wall,  the  ventricular  septum. 
The  two  auricles  are  not  separated.  The  opening  be- 
tween the  two  auricles  is  the  foramen  ovale.  Is  there  any 
trace  of  the  formation  of  the  auricular  septum? 

Draw  a  diagram  of  the  circulatory  system  in  the  thorax 
as  you  have  found  it  in  your  dissection.  Label  all  the 
parts. 

Trace  the  lungs  to  the  mouth.  Trace  the  oesophagus 
to  the  mouth.  What  is  the  relation  of  the  oesophagus 
to  the  trachea  and  larynx? 


INDEX 


Abdomen  of  pig,  dissection  of,  39 
Achromatin,  i 

Acustico-facialis  ganglion,  29,  34 
Air-chamber,  12,  13 
Alimentary    tract   and   its   append- 
ages,  reconstruction   of  in 
chick     of     sixty-eight     to 
seventy-two    hours'    incu- 
bation, 31 

Allantois,  28,  30,  32,  38 
Amnion,  24,  25,  26,  38,  39 
Amphibia,  8 
Amphioxus,  8 
Anaphases,  2,  7 
Animal  pole,  10 
Anterior  cardinal  vein,  25,  26 
Aorta,  caudal,  41 

dorsal,  20,  21,  24,  35,  41 

ventral,  17,  20,  24 
Aortic  arch,  24 
Archenteron,  n 
Area  opaca,  14,  15,  16 

pellucida,  5,  14,  15,  16 

vasculosa,  14,  15 
Artery,  carotid,  35,  43 

gastric,  41 

hepatic,  41 

iliac,  41 

innominate,  43 

pulmonary,  42 

renal,  41 

subclavian,  43 

superior  mesenteric,  41 

umbilical,  36,  39,  41 

vitelline,  14,  22 
Artbropoda,  9 


Ascaris,  6,  7 

Auditory  vesicle,  22,  25,  29 
Auricles,  35,  42 
Auricular  septum,  43 

-ventricular  valves,  35 

Blastoderm,  12,  14,  15,  18,  20,  22 

Blastopore,  n 

Blastula,  n 

Blood  islands,  16 

Body  cavity,  embryonic,  19,  26 
extra-embryonic,  19 

Brachial  plexus,  35 

Brain,  15 

fore-brain,  16,  21,  28,  32,  34 
hind-brain,  17,  25,  28,  32,  34 
mid-brain,  16,  21,  32 

Broad  ligament,  37 

Cardiac  region,  33 
Cardinal  veins,  anterior,  25 

posterior,  25 
Carotid  artery,  35  N- 
Caudal  aortae,  41 
Cell,  division,  i 

parts  of,  i 

in  astroid  stage,  2 

in  diastroid  stage,  2 

in  di-spireme,  3 

in  metaphase,  2 

in  resting  stage,  i 

in  spireme  stage,  i 
Cells,  stroma,  5 

follicular,  5 
Cell-wall,  i 


45 


46 


INDEX 


Centrosome,  i,  2 

Cephalic  flexure,-  22,  23 

Cerebellum,  28 

Cerebral  hemispheres,  28,  32,  35 

Cervical  flexure,  28 
sinus,  33 

Chalazae,  12 

Chick  embryo,  15,  16 

Choroid  fissure,  22,  29,  34,  35 

Chorion,  24,  38 

Chromatin,  i,  3,  6 

Chromosomes,  2,  6 

Circulatory    system,    reconstruction 
of  in  chick  of  thirty-three 
to  thirty-eight  hours'  incu- 
bation, 21 
of  forty-four  hours' incubation,  27 

Cleavage,  kinds  of,  8 
stages  of,  10 

Coelome,  19,  20,  26 

Colon,  descending,  40 

Common  bile  duct,  41 

Corona  radiata,  5 

Corpora  lutea,  38 

Cyclostomata,  8 " 

Cytoplasm,  i,  3,  6,  7,  9,  12    ' 

Cystic  duct,  40 

Daughter  cells,  3 
Descending  colon,  40 
Deutoplasm,  4 
Diaphragm,  41,  42 
Diaster,  3 
Diencephalon,  28 
Discoidal  cleavage,  9 
Discus  proligerus,  5 
Dissection  of  pig  embryo,  39 
Dorsal  aorta,  20,  21,  24,  35,  41 

mesentery,  30 

zone  of  spinal  cord,  34 
Duodenum,  32 


Duct  of  Cuvier,  26,  35 

of  Wirsung,  41 
Dyad,  6 

Echinodermata,  8 
Ectoderm,  18,  19,  20 
Egg,  cleavage  of,  8 

fertilization  of,  7 

formation  of,  4 

hard-boiled,  13 

hen's,  12 

incubated,  14 

maturation  of,  6 

parts  of,  4 

raw,  12 
Embryo  of  chick,  fixed  and  stained, 

15 

transverse  sections  of,  17,  23, 
29 

live,  14 

whole  mount,  15,  16,  21,  27 
of  pig,  dissection  of,  39 

pregnant  uterus,  37 

ten  millimeter,  32 

transverse  sections,  34 

whole  embryo,  32 
Embryonic  body  cavity,  19 
Endocardium  19,  26 
Endoderm,  18,  19,  20 
Endolymphatic  duct,  34 
Epiblast,  1 8 
Epiphysis,  28 
Equal  cleavage,  9 
Evagination,  18 
External  auditory  meatus,  33 
Extra-embryonic    body    cavity,    19, 

20 

Eye,  lens  of,  22,  23,  30,  32,  35 

Fallopian  tube,  37,  40 
Fertilization,  3 


INDEX 


47 


Follicular  cavity,  5 

cells,  4,  5. 

fluid,  5 

Foramen  ovale,  43 
Fore-brain,  16,  19,  21,  28,  32,  34 

-gut,  30 

-limb  buds,  30,  33,  36 
Frog's  eggs,  10 

Gall-bladder,  40 

Ganglion,  acustico-facialis,  29,  34 

glosso-pharyngeal,  29 

petrosal,  35 

trigeminal,  34 

vagus,  34 
Gastric  artery,  41 
Gastrula,  n 
Gastrulation,  n 
Genital  ridge,  36 
Germinal  epithelium,  4 

spot,  4,  9 

vesicle,  4,  9 
Germ  layers,  18 
Gill  arches,  24,  35 

clefts,  23,  24,  33,  35 

slits,  23 

Glosso-pharyngeal  ganglion,  29 
Graafian  follicle,  4,  6,  38 

young,  4 

ripe,  5 
Growth  period,  6 

Hard-boiled  egg,  13 
Head  cap,  3 

-fold,  15 

Heart,  14,  17,  19, ,25,  26,  28,  42 
Hepatic  artery,  41 

duct,  41 
Hind-brain,  17,  25,  28,  32,  34 

-gut,  28,  30 

-limb  buds,  31,  33,  36 
Holoblastic  cleavage,  8,  9 


Horns  of  uterus,  37 
Hyoid  arch,  23 
Hyomandibular  cleft,  23 
Hypoblast,  18 
Hypophysis,  25,  31 

Iliac  artery,  41 

veins,  41 

Incubated  egg,  14 
Inferior  vena  cava,  36 
Innominate  artery,  43 
Intermediate  cell  mass,  20 
Intestine,  40,  41 
Invagination,  18 
Isthmus,  28 

Jugular  vein,  34 

Karyokinesis,  3 
Kidneys,  40 

Lachrymal  groove,  32 

Larynx,  43 

Lateral  folds,  22 

plates,  20,  22,  23 
limiting  sulcus,  26 

Lens  of  eye,  22,  23,  30,  32,  35 

Liver,  32,  36,  39 

diverticulum,  30 

Lung  buds,  30 

Lungs,  43 

Major  omentum,  36 
Mammalia,  8 
Mandibular  arch,  23 

process,  33 
Maturation,  6 
Matured  ovum,  7 
Maxillary  nerve,  35 

process,  33 

Medulla  oblongata,  28 
Meroblastic  cleavage,  9 
Mesencephalon,  28 


48 


INDEX 


Mesentery,  41 

dorsal,  30 

ventral,  30 
Mesoblast,  18 
Mesoblastic  somites,  15,  20 
Mesoderm,  18,  20 
Mesonephric  duct,  26 
Metaphase,  2,  6,  7 
Metencephalon,  28 
Mid-brain,  16,  17,  21,  32 

-piece,  3  - 

Milk  ridge,  33 
Minor  omentum,  36 
Mitosis,  3 
Monad,  7 
Muscle-plate,  25 
Muscular  segment,  33 
Myelencephalon,  28 
Myelon,  17 
Myocardium,  19,  26 
Myotome,  25  * 

Nephrotome,  20,  26 
Nerve,  maxillary,  35 

ninth,  35 

spinal  accessory,  34,  35 

vagus,  35 
Neural  groove,  15 

plates,  15 

tube,  1 6,  17 
Neuromores,  34 
Ninth  nerve,  35 

Notochord,  15,  17,  20,  21,  23,  34 
Nuchal  flexure,  28 
Nuclear  membrane,  i 
Nucleolus,  i 
Nucleus,  i,  2,  8,  9 

of  Pander,  13 

(Esophagus,  32,  35,  43 
Olfactory  pit,  28,  33 
Oocyte,  7 


Optic  cup,  22,  32 

stalk,  23,  29,  34,  35 
vesicles,  16,  19,  22,  23,  29 

Oral  pit,  23 

Ostium  tubae  abdominale,  37 

Otocyst,  34 

Ovaries,  4,  38,  40 

Ovary  of  cat,  4 

Oviduct,  37 

Ovum,  formation  of,  4 

Pancreas,  41 
Pancreatic  duct,  41 
Pericardium,  42 
Peripheral  cleavage,  9 
Petrosal  ganglion,  35 
Pharynx,  20,  25,  35 
Pig  embryo,  ten  millimeter,  trans- 
verse sections,  34 

whole,  32 

dissection  of,  39 
Polar  body,  7 

Posterior  cardinal  vein,  25,  26 
Pregnant  uterus,  39 
Primitive  streak,  16,  17,  21,  23 
Pronucleus,  7,  8 
Prophases,  2 
Pulmonary  arteries,  42 

veins,  43 

Raw  egg,  12 

Reconstructions  of  circulatory  sys- 
tem of  chick  of  thirty- 
three  to  thirty-six  hours' 
incubation,  21 

of  circulatory  system  of  chick 
of     forty-four     to     forty- 
eight  hours'  incubation,  27 
of    central    nervous    system    of 
chick    of    forty-four    to    forty- 
eight  hours'  incubation,  27 


INDEX 


49 


Reconstructions  of  alimentary  tract 
and  it  appendages  in 
chick  of  sixty-eight  to 
seventy-two  hours'  incu- 
bation, 31 

Rectum,  40 

Renal  arteries,  41 
veins,  42 

Retina,  22,  35 

Sclerotome,  25 

Sections  of  chick  embryo,  transverse, 
thirty-three  to  thirty-six 
hours'  incubation,  17 
forty-four        to      forty-eight 

hours'  incubation,  23 
sixty-eight     to     seventy-two 

hours'  incubation,  29 
of    ten    millimeter    pig,    trans- 
verse, 34 

Segmental  plate,  16 
Segmentation,  8 

cavity,  n 

Septum  spurium,  36 
Shell  membrane,  1 2 
Sinus  pocularis,  40 
Somatopleure,  19,  26 
Somites,  15,  20 
Spermatozoon,  8 

parts  of,  3 

Spinal  accessory  nerve,  34,  35 
cord,  15,  17,  34 
dorsal  zone,  34^ 
ventral  zone,  34 
Spindle  fibers,  2,  7 
Spireme,  i,  2 
Splanchnopleure,  19 
Spleen,  41 
Starfish  egg,  9 
Stomach,  36 
Stratum  granulosum,  5 


Stroma,  5 
Subclavian  artery,  43 

vein,  35 
Superior  mesenteric  artery,  41 

vena  cava,  43 

Tail,  3,  15,  33 

Telencephalon,  28 

Telophases,  3 

Testes,  40 

Tetrad,  6 

Thalamencephalon,  28 

Theca  folliculi,  5 

Thorax  of  pig,  dissection  of,  42 

Thyroid  gland,  31 

Trachea,  31,  35 

Transverse      sections      of      chick, 

thirty-three     to     thirty-six 

hours'  incubation,  17 
forty-four       to       forty-eight 

hours'  incubation,  23 
sixty-eight     to     seventy-two 

hours'  incubation,  29 
of  ten  millimeter  pig,  34 
Trigeminal  ganglion,  34 

Umbilical  artery,  36,  39 

cord,  33,  36,  38 

vein,  36,  39,  40 
Unequal  cleavage,  10 
Urethra,  40 
Ureter,  39 
Uterus,  horns  of,  37 
Urinary  badder,  39 

Vagina,  37,  40 
Vagus  ganglion,  34 

nerve,  35 
Vascular  area,  16 
Vas  deferens,  40 
Vegetative  pole,  10 


INDEX 


Veins,  anterior  cardinal,  25,  26 

posterior  cardinal,  25,  26 

iliac,  41 

inferior  vena  cava,  36,  42 

jugular,  34 

pulmonary,  43 

renal,  42 

superior  vena  cava,  43 

subclavian,  35 

umbilical,  36,  39,  40,  42 

vitelline,  14 
Ventral  aorta,  17,  20,  24 

mesentery,  30 

zone  of  spinal  cord,  35 
Ventricular  septum,  35,  43 
Ventricles,  35,  42 
Visceral  arches,  24 

clefts,  23 

pouches,  23 
Vitelline  arteries,  14,  22 

membrane,  4,  5,  12,  13 

veins,  14,  17 


White  yolk,  13 

Whole   embryo   ten   millimeter  pig, 

32 

Whole     mount     of    chick    embryo, 
twenty-two      to      twenty- 
four  hours'  incubation,  15 
thirty-three         to         thirty-six 

hours'  incubation,  16 
forty-four  to  forty-eight  hours' 

incubation,  21 
sixty-eight       to       seventy-two 

hours'  incubation,  27 
Wolffian  body,  30,  36,  40 
duct,  26,  30 


Yellow  yolk,  13 
Yolk,  4,  8,  12,  13,  14,  15,  18 
sac,  24 


Zona  pellucida,  5 


THIS  BOOK  IS  DTJE  ON  THE  1M*  DATE 
STAMPED  BELOW 

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THE    SEVENTH    DAY 


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